The present technology relates to an optical device for performing dimming by controlling the transmittance of light passing through a cell and an imaging device including the optical device.
For a dimming control in an imaging device, there are proposed various dimming cells capable of freely and electrically varying the transmittance of incident light. Among them, there are proposed a number of dimming cells using a liquid crystal. In such dimming cells, a guest-host (GH) type liquid crystal containing a dichroic dye is often used. The dimming cell is typically disposed at a portion where known iris diaphragms has been disposed, or a periphery portion of an imaging element.
However, when dimming is performed by disposing a dimming cell using the GH type liquid crystal on the optical path, since the GH type liquid crystal contains a dye, light is absorbed by the dye, and the maximum light transmittance of the dimming cell is decreased. This phenomenon is significant particularly when a GH type liquid crystal prepared for dark state is used, and as a result, an F number of a lens is dropped.
In order to solve such an issue, in Japanese Unexamined Patent Application Publication No. 2005-109630, a dimming control is performed such that a dimming cell containing a GH type liquid crystal is displaced from the optical axis at the time of low illumination imaging (for example, at the time of taking an image of dark scene).